The present invention relates to a breathable woven fabric of thermoplastic polymeric tapes and sacks made thereform. The term "breathable" refers to the ability of the fabric to allow gases and moisture to pass freely through the fabric.
Breathable woven fabrics are useful in packaging applications, particularly for making sacks intended to contain finely divided solid agricultural products such as seed.
Woven tape structures have previously been prepared from oriented tapes of polypropylene or polyethylene. Structures of this type may exhibit a tendency to unravel or the weave may tend to distort, both of which may affect the utility of the woven structure in some end uses. Techniques have previously been suggested for the stabilization of such woven structures. For example, the use of coatings is described in Luckenhaus, British Pat. No. 1,185,553.
For some applications, however, it is desirable to retain the breathable nature of an uncoated woven fabric, for example, when the fabric is used for agricultural sacks or tarpaulins. One method for obtaining a breathable sack disclosed in Overton, Canadian Pat. No. 909,726 involves inserting a plastic liner, punctured with a plurality of small holes, into a sack woven from oriented plastic tapes. In general, however, such methods are commercially inefficient.
For packaging granular or finely divided solids e.g., fertilizer or seed, in sacks of woven structures it is desirable not only to provide a sack which is breathable but also to ensure that the weave of the structures is stable and does not exhibit a tendency to open.
Techniques for stabilization of woven structures are shown in Poole, U.S. Pat. No. 3,951,050 in which tubes of woven structures, made from polyethylene tapes, are coated with a thin layer of polyethylene. Other techniques, which retain the breathable nature of the structure, for example, by use of an adhesive, are described in Foster, U.S. Pat. No. 2,521,055. Such techniques, however, tend to be expensive or require facilities in addition to the weaving and coating facilities normally available to manufacturers of fabric woven from thermoplastic polymeric tapes.